1. Field
One embodiment of the invention relates to a method of recording or reproducing an encryption key or the like, information requested to have a high confidentiality. This invention further relates to a reproducing apparatus which uses stored or recorded highly confidential data.
2. Description of the Related Art
In recent years, various reproducing apparatuses capable of reproducing AV contents recorded on a disc medium, such as a DVD (Digital Versatile Disc), have been developed. Such reproducing apparatuses include a recorder with a dedicated player or a reproducing function, and a personal computer provided with a DVD disc drive and a reproducing software program. Stream data recorded on a DVD disc or the like to be played back on such a reproducing apparatus is encrypted to prevent the data from being copied. An encryption scheme conforming mostly to the CCS (Content Scramble System) method has been applied to the encrypted stream data part. As a higher encryption scheme, AACS (Advanced Access Content System) has been proposed (refer to Jpn. Pat. Appln. KOKAI Publication No. 2005-39480). When the AACS method is used, for example, a reproducing apparatus set manufacturer gets a specific key set from a key tree the licenser has, encrypts different combinations of keys, and incorporates the encrypted keys into individual reproducing apparatuses.
In the AACS, each of a plurality of title keys is encrypted using a device key and a random number generated which have been assigned to each recording and reproducing apparatus capable of recording and reproducing contents rightfully, such as a DVD recorder, and is registered together with the random number in a title key file, which is then recorded on a DVD medium. When the title contents are reproduced, the encrypted title key registered in the title key file is decrypted using the random number and the device key of the recording and reproducing apparatus to be reproduced and the title contents are decrypted using the decrypted title key, thereby reproducing the title contents.
Content protection using such a title key is a technology for effectively preventing unauthorized use of DVD media contents. To maintain such functionality, the title key file has to be updated as a result of re-encrypting the title key. Since the title key is updated by writing the title key file onto a disc, frequent updating of the title key file leads to a decrease in the response of the system.
Since the title key file has to be updated according to the AACS method, a different update condition is used, depending on the type of media (such as rewritable media or write-once media).